Air Filter Element and Air Filter

ABSTRACT

Disclosed are an air filter element, a filter housing, and an air filter in which the air filter elements have a high filtering capacity and a long service life by increasing the filter surface of an air filter element taking into account structural requirements for the air filter housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a bypass continuation application of internationalapplication No. PCT/EP2013/050585 having an international filing date ofJan. 14, 2013 and designating the United States, the internationalapplication claiming a priority date of Jan. 13, 2012, based on priorfiled German patent application No. 10 2012 000 490.7, the entirecontents of the aforesaid international application and the aforesaidGerman patent application being incorporated herein by reference.

FIELD OF THE INVENTION

Invention relates to the technical field of the preparation andfiltration of air for example the air filtration in a motor vehicle, aconstruction machine, or an agricultural machine. In particular, theinvention relates to an air filter element and an air filter.

TECHNICAL BACKGROUND OF THE INVENTION

For example, air filters are used in the air supply of internalcombustion engines in order to remove pollutants and dirt particles fromthe air supplied for the combustion so that only purified air issupplied to a combustion process in the internal combustion engine.

An air filter has an inflow opening for unpurified, dirty air and anoutflow opening for the filtered, clean air; the filter element performsthe actual filtering function. The air supply of the internal combustionengine is provided via the outflow opening of the air filter; theinternal combustion engine takes in the required air or air quantity.The filter element or air filter element is composed of a filter mediumsuch as a filter paper through which the air that is to be filteredflows when the internal combustion engine sucks air in so that the dirtparticles contained in the air flowing through are separated or removedin the filter medium.

Usually, the filter medium is folded (folded filter) or has a multitudeof filter chambers (fluted filter) in order to increase the surface areaof the filter, which also extends the service life of an air filterelement since a larger filter surface area can absorb more dirtparticles before the pressure drop at the filter medium caused byseparated dust has become so significant that the air is no longerallowed to pass through to the internal combustion engine in therequired quantity and the air can no longer pass or flow through thefilter medium.

Usually, the filter element is contained in the housing and, forexample, a functional component in the form of an additional filterelement is provided in the housing, upstream of the outflow opening ofthe air filter. The additional filter element in this case performs thefunction of preventing dirty air from flowing into the internalcombustion engine through the air filter, even if the air filter hasbeen removed from the housing. For this reason, a main element or airfilter element and a functional component must usually be placed insidethe housing of the air filter.

In addition, the structural design of the housing can be adapted toexternal circumstances, e.g. the spatial circumstances inside the enginecompartment of a motor vehicle. The structural design of the housing hasa direct influence on the size of the air filter element and thereforeon the filtration performance of the air filter element.

Depending on the volume inside the air filter housing occupied by thefunctional component, the main element or air filter element iscorrespondingly reduced in size and/or the depth of the air filter foldsor filter chambers of the main element is adapted so as to divide upspace inside the air filter housing.

Usually, the folds of the filter element are folded or the depths of thefilter chambers are embodied so that they are equal in depth and thusconstitute a block-shaped air filter element. This can, however, resultin the fact that the functional component does not take up the entirespace that the block-shaped design of the main element leaves open onthe inside of the housing.

WO 98/47601 has disclosed a filter element in the form of a foldedfilter element for an air filter; the filter element is composed of afilter insert embodied in zigzag form.

SUMMARY OF THE INVENTION

One object of the invention can be viewed as achieving a high filtrationperformance and a long service life of air filter elements by enlargingthe filter area of an air filter element while taking into accountstructural requirements of the air filter housing.

The invention discloses an air filter element and an air filteraccording to the features of the independent claims. Modifications ofthe invention ensue from the dependent claims and the followingdescription.

Another embodiment of the invention discloses an air filter element withan upstream surface, a downstream surface, and a filter medium; thefilter medium extends between the upstream surface and downstreamsurface; at least one or both of the upstream surface and downstreamsurface has a recessed offset at least in some sections; a functionalcomponent, which is to be brought into a functional relationship withthe air filter element, can protrude at least partially into a freespace produced by the recessed offset; the functional component, whichis to be brought into a functional relationship with the air filterelement, can have a functional relationship with the recessed offset ofthe upstream surface or downstream surface.

For example, the filter medium can contain or be composed of paper,nonwoven, microfiber material, nanofiber material, or plastic or can becomposed of a mixture or composite of these materials.

The recessed offset is an offset of a flow surface (upstream surface ordownstream surface) in the direction toward the opposite flow surface,where the recessed offset is still part of the flow surface. A recessedoffset can in particular be formed by a bend, a step, a bulge, or arecess; in particular, the recessed offset can be composed of the freevolume or the concave indentation of a flow surface.

A functional component has a functional relationship with the air filterelement, for example, if the two components are matched to each otherfor a filtering procedure or the filtering procedure only occurs througha cooperation of these components. The functional component and airfilter element are also in a functional relationship if in addition topure filtration, the functional component performs another function suchas chemical filtration or guidance of the air flow. In this case inparticular, the structural design of the functional component and of theair filter element can be matched to each other so that the respectivesurfaces of these components correlate to one another, which enablesmaximum use to be made of the space that is available for the air filterelement and functional component.

According to another embodiment of the invention, at least one or bothof the upstream surface and downstream surface has a recessed offsetwith a one-dimensional concave or convex form.

In particular, the air filter element can be formed in a simple way outof a single, continuous medium web, since the one-dimensional concave orconvex form—as opposed to a two-dimensional one—can be produced simplyby means of a variable fold edge spacing in the folding of the filtermedium.

According to another embodiment of the invention, the filter medium is afilter medium that is folded out of folds; the folds each have a firstfold leaf and second fold leaf, which adjoin each other at a fold edgeby means of their respective fold leaf edges; the first fold leaves ofadjacent folds lie essentially parallel to each other; the first andsecond fold leaves extend between the upstream surface and thedownstream surface; and the recessed offset extends along a direction inwhich the fold edges extend.

As a result, as described above and below, the air filter element makesit possible to provide a large filter area and to adapt to thestructural circumstances of the use environment since the recessedoffset makes it possible to configure the outer geometric shape of theair filter element.

According to another embodiment of the invention, the fold depth variesin a direction transverse to the direction of the fold edges. Inparticular, the fold depth varies between adjacent folds.

In this case, the fold depth of a filter fold is constant in a directionextending along the fold edge.

According to another embodiment of the invention, the filter element hasa support structure. In particular, the support structure also serves tolaterally seal the folds. Preferably, the support structure has arecessed offset, particularly in the form of an indentation, which atleast partially corresponds to a shape of the recessed offset of theupstream surface or downstream surface. As a result, at least along therecessed offset, the support structure has a recessed offset thatcorresponds to the recessed offset or has a corresponding indentation sothat the support structure presents as little as possible obstruction toan air flow into and/or out of the recessed offset.

According to another embodiment of the invention, the fold leaves arelaterally embedded in the support structure at the fold leaf edges thatdo not adjoin fold leaf edges of respectively adjacent filter leaves. Itis thus possible to increase a mechanical strength of the air filterelement.

According to another embodiment of the invention, the folds extendingacross the recessed offset are produced from a continuous medium web. Asopposed to an air filter element composed of a plurality of medium webs,there is thus no glue seam or joining seam and instead, the filtermedium is produced from continuous material.

According to another embodiment of the invention, adjacent fold leavesare reciprocally stabilized by means of at least one spacer device. Thespacer device can in particular be made of a plastic. For example, themolten plastic for producing the spacer device is applied to the filtermedium. Preferably, the spacer device has glue beads or glue lines. Thespacer device, in particular the glue lines, is/are situated on thedownstream and/or upstream side of the filter medium.

The spacer device or glue lines can be arranged perpendicular ordiagonal to the upstream surface or downstream surface. In addition, theglue lines or glue beads can have a continuous glue bead or a broken ordotted glue bead and can be composed of a plurality of glue beadsegments. In this case, the glue line segments or glue bead segments canbe offset from one another so that the broken bead encloses an angle ofbetween 1° and 90° with the fdd edges and/or the upstream surface ordownstream surface.

The spacer device in this case can, for example, ensure that the foldleaves maintain a certain distance from one another and in particular,the spacer device can cause an opening angle of the filter folds toremain the same. This can facilitate a uniformly high filtrationperformance of the air filter element since the fold openings can changeby only a small amount due to the presence of the glue lines.

In particular, the spacer device, particularly in the form of gluelines, prevents a decrease in the size of the filter opening. The foldleaves of a filter fold can only move toward each other by a reducedamount due to the presence of the spacer device inserted between them.

According to another embodiment of the invention, the spacer device,particularly in the form of glue beads or glue lines, extends parallelto the fold leaf edges that do not adjoin fold leaf edges ofrespectively adjacent filter leaves.

As a result, in at least some sections, the spacer device extends in adirection from the upstream surface to the downstream surface and viceversa and parallel to the support structure. As a result, it presentsthe air flow with the least possible amount of flow resistance.

Another embodiment of the invention discloses an air filter elementdevice with an air filter element, as described above and below, and afunctional component; the functional component protrudes at leastpartially into the free space produced by the recessed offset and thereis a functional relationship between the functional component and therecessed offset of the upstream surface or downstream surface.

As a result, a functional component can interact with an air filterelement, for example in that the two components are situated inside anair filter housing, and because the free space is configured inaccordance with the dimensions of the functional component, it causes aslittle loss as possible to the filter area of the air filter element,thus maximizing the filter area despite the accommodation of afunctional component in the air filter housing.

According to another embodiment of the invention, the functionalcomponent has an interface surface; in at least some sections, theinterface surface has a shape that corresponds to that of the recessedoffset of the upstream surface or downstream surface. In particular,this makes it possible for the functional component to be adaptedstructurally and geometrically to the air filter element. In this case,the area or surface of the functional component oriented toward the airfilter element is referred to as the interface surface.

According to another embodiment of the invention, the support structurecovers the filter medium laterally the recessed offset. As a result, thesupport structure seals the filter medium at the surface of the airfilter element that is oriented perpendicular to the fold edges.

According to another embodiment of the invention, the support structurehas a first retaining surface and a second retaining surface; therecessed offset is embodied on the support structure between the firstretaining surface and the second retaining surface of the supportstructure.

As a result, upon insertion into an air filter housing, the firstretaining surface and the second retaining surface have a greaterpenetration depth than the recessed offset on the support structure andthe filter medium or air filter is thus retained by the first and secondretaining surface.

The first retaining surface and second retaining surface can also beshaped almost in the form of a point or be embodied as point-shaped,i.e. have very small geometric dimensions of less than 1 cm².

According to another embodiment of the invention, the upstream ordownstream surface of the filter medium associated with the recessedoffset on the support structure extends into a region lateral to therecessed offset on the support structure. For example, the regionlateral to the recessed offset on the support structure is the regionbetween the first retaining surface or the second retaining surface andthe maximum depth of the recessed offset on the support structure, inthe form of an indentation. Because the upstream or downstream surfaceextends into the region lateral to the recessed offset on the supportstructure or lateral to the indentation, the surface of the filtermedium can be maximized despite the presence of the recessed offset orindentation.

According to another embodiment of the invention, the support structurehas a (third) retaining surface, which is situated, for example, betweenthe first retaining surface and second retaining surface in the recessedoffset on the support structure. As a result, particularly in additionto the first and second retaining surface, an additional (third)retaining surface is situated, for example, in the indentation on aretaining surface recess in an air filter housing and can provide animproved positioning and fixing of the air filter element in the airfilter housing.

According to another embodiment of the invention, at least one of thefirst, second, and third retaining surfaces absorbs a retaining force inthe direction along the plane of the support structure. As a result, theretaining surface or surfaces provide(s) for a positioning or fixing ofthe air filter element in an air filter housing. The retaining surfacesabsorb a retaining force along or parallel to the plane of the supportstructure, particularly in a direction in which the air flows throughthe air filter from the upstream surface to the downstream surface.

According to another embodiment of the invention, in at least somesections, the upstream or downstream surface associated with therecessed offset on the support structure has a one-dimensional concaveor convex form; in at least some sections, the curvature of the concaveor convex form corresponds to that of at least a part of the recessedoffset.

The above explanations of the one-dimensional concave or convex formthat can increase the filter area apply analogously to theone-dimensional concave or convex form of the recessed offset and thedownstream and upstream surface.

The fact that the respective first fold leaf edges of adjacent folds areoriented essentially parallel to one another means that the folds areoriented in essentially the same direction, which in turn means that thedirection of air flow through the folds extends in essentially the samedirection.

According to another embodiment of the invention, the upstream ordownstream surface associated with the recessed offset has a shape thatcorresponds to at least a part of the recessed offset of the supportstructure, in that it is provided with a plurality of folds of varyingfold depths.

At least some of the plurality of folds with varying fold depths isadvantageously produced from a continuous filter medium web. It istherefore unnecessary to combine several partial filters to produce anair filter element and, because of the variable fold depth of the foldsin comparison to one another, it is possible, for example, to produce acurved upstream or downstream surface.

Another embodiment of the invention discloses an air filter with an airfilter housing, an air filter element, and a functional component; theair filter element has an upstream surface, a downstream surface, and afilter medium; the filter medium extends between the upstream surfaceand downstream surface; at least one or both of the upstream surface anddownstream surface has a recessed offset; the functional componentprotrudes at least partially into the free space produced by therecessed offset; and the functional component has a functionalrelationship with the recessed offset at the upstream surface anddownstream surface of the air filter element.

The recessed offset permits a structural adaptation or an adaptation tothe geometrical form of the air filter housing, the air filter element,and the functional component.

According to another embodiment of the invention, the recessed offset onthe downstream surface or upstream surface has a one-dimensional concaveor convex form. Conversely, the functional component can have a convexor concave form so that the geometric forms of the air filter elementand functional component are matched to each other, making maximum useof the available space in an air filter housing.

According to another embodiment of the invention, the functionalcomponent has an interface surface; in at least some sections, theinterface surface has a shape that corresponds to that of the recessedoffset of the upstream surface or downstream surface. Analogously forthe shape of the interface surface as well, its adaptation to therecessed offset can permit maximum use of the available space in the airfilter housing.

According to another embodiment of the invention, the functionalcomponent is embodied as an additional filter element that protrudes atleast partially into the free volume produced by the recessed offset;the additional filter element has an upstream surface and a downstreamsurface; one or both of the upstream surface and downstream surface ofthe additional filter element corresponds to one or both of the upstreamsurface and downstream surface of the air filter element. In particular,the additional filter element can be embodied as a prefilter orafterfilter and can thus be in a functional relationship with either theupstream surface or downstream surface; the corresponding flow surfaceor also both flow surfaces has/have a recessed offset on the air filterelement. The prefilter can, for example, be embodied to perform aprefiltration of the air. The afterfilter can be embodied to ensure thefiltering function of the air filter even if, during a replacement ofthe air filter element, air continues to flow through the air filter oralso in the event of a fault, e.g. if the filter web of the air filterelement is damaged. The recessed offset in the air filter element allowsit to be placed in the filter housing in a space-saving way togetherwith the prefilter and/or after filter.

According to another embodiment of the invention, the functionalcomponent is embodied as a baffle device that protrudes at leastpartially into the free volume produced by the recessed offset; thebaffle device has at least one baffle surface whose baffle surface edgeis oriented toward the respective upstream surface or downstream surfaceof the air filter element. The baffle device can improve an inflowand/or outflow of air into and/or out of the air filter.

According to another embodiment of the invention, functional componentis embodied as a flow straightener; the flow straightener is associatedwith an air mass sensor that is to be brought into a functionalrelationship with the air filter element; and the flow straightenerprotrudes at least partially into the free volume produced by therecessed offset.

According to another embodiment of the invention, the functionalcomponent is embodied as a housing support rib; the housing support ribhas a retaining surface for retaining the air filter element; thehousing support rib protrudes at least partially into the free spaceproduced by the recessed offset. The housing support rib in thisinstance can be an indentation in the housing wall. The retainingsurface can be embodied to accommodate the support structure or aretaining surface recess of the support structure when the air filterelement is inserted into the air filter housing so that the retainingsurface establishes or predetermines the position of the air filterelement in the air filter housing.

According to another embodiment of the invention, the functionalcomponent is embodied as a partition wall; the partition wall protrudespartially into the housing; the partition wall protrudes at leastpartially into the free space produced by the recessed offset and has asealing surface that divides the filter housing with the air filterelement into two filter chambers on the upstream side, which each have aseparate inflow opening. In particular, an inflow opening is providedwith a valve device.

As a result, the partition wall makes it possible to provide a pluralityof inflow openings so that for example if a filter becomes clogged orexcessively dirty, air is taken in via the second filter chamber.

According to another embodiment of the invention, the functionalcomponent is embodied as an adsorption filter element for hydrocarbonsthat protrudes at least partially into the free volume that is producedby the recessed offset. As a result, a filter air can also be subjectedto a chemical filtration, with both filtering procedures taking placeinside the same air filter housing. Primarily, however, an adsorptionfilter element for hydrocarbons situated on the downstream side servesto capture hydrocarbons that could diffuse through the air filter andinto the ambient air when the internal combustion engine is not running.It is also possible for a plurality of adsorption filter elements forhydrocarbons to be accommodated in a plurality of free volumes.

According to another embodiment of the invention, the functionalcomponent is embodied as a resonator geometry that protrudes at leastpartially into the free volume that is produced by the recessed offset.The resonator geometry makes it possible to damp noise in the air flowflowing through the air filter; the noise damping takes place directlyat the location in which the flow noise is generated, namely on theinside of the air filter housing.

The air filter element and the air filter, as described above and below,are in particular used for air filtration in motor vehicles,construction machines, or agricultural machines. In particular, they areused for filtering the intake air of an internal combustion engine orfiltering the intake air of a vehicle's passenger compartment. They can,however, also be embodied in a modified way so that they can also beused for other fluids, in particular for liquids and liquid mixtures. Inthis regard, they can in particular be largely the same in structure,but embodied as fuel or oil filter elements for motor vehicles or asfuel or oil filters for motor vehicles.

The individual features can naturally be combined with one another,sometimes achieving advantageous effects that go beyond the sum of theirindividual effects.

Exemplary embodiments of the invention will be described below withreference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 2 shows a side view of an air filter element according to anexemplary embodiment of the invention.

FIG. 3 shows a sectional view of an air filter according to an exemplaryembodiment of the invention.

FIG. 4 shows a sectional view of an air filter element and a functionalcomponent according to an exemplary embodiment of the invention.

FIG. 5A shows a cross section through an air filter element according toan exemplary embodiment of the invention.

FIG. 5B shows a cross section through an air filter element according toan exemplary embodiment of the invention.

FIG. 5C shows a cross section through an air filter element according toan exemplary embodiment of the invention.

FIG. 5D shows a cross section through an air filter element according toan exemplary embodiment of the invention.

FIG. 5E shows a cross section through an air filter element according toan exemplary embodiment of the invention.

FIG. 5F shows a cross section through an air filter element according toan exemplary embodiment of the invention.

FIG. 5G shows a cross section through an air filter element according toan exemplary embodiment of the invention.

FIG. 6 shows a cross section through a fluted filter according to anexemplary embodiment of the invention.

FIG. 7 shows an air filter element and a functional component accordingto an exemplary embodiment of the invention.

FIG. 8 shows an isometric, exploded view of an air filter with an airfilter element, a housing, and a functional component according to anexemplary embodiment of the invention.

FIG. 8A is an isometric depiction of an air filter with an air filterelement, a housing, and a functional component according to an exemplaryembodiment of the invention.

FIG. 9 shows a sectional view of an air filter according to an exemplaryembodiment of the invention.

FIG. 9A shows a sectional view of an air filter according to anexemplary embodiment of the invention.

FIG. 9B shows a sectional view of an air filter according to anexemplary embodiment of the invention.

FIG. 10 is an isometric depiction of an air filter according to anexemplary embodiment of the invention.

FIG. 10A is an isometric depiction of an air filter according to anexemplary embodiment of the invention.

FIG. 11A is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 11B is an isometric depiction of a functional component for an airfilter according to an exemplary embodiment of the invention.

FIG. 11C is an isometric depiction of a housing of an air filteraccording to an exemplary embodiment of the invention.

FIG. 12A is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 12B is an isometric depiction of a functional component for an airfilter according to an exemplary embodiment of the invention.

FIG. 13A is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 13B is an isometric depiction of a functional component for an airfilter according to an exemplary embodiment of the invention.

FIG. 13C is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 13D is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 14 shows a sectional view of an air filter with a main element, afunctional component, and a housing according to an exemplary embodimentof the invention.

FIG. 15 is an isometric depiction of an air filter according to anexemplary embodiment of the invention.

FIG. 16 shows a sectional view of an isometric depiction of an airfilter according to an exemplary embodiment of the invention.

FIG. 17 shows a sectional view of an air filter according to anexemplary embodiment of the invention.

FIG. 18 is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 19 shows a sectional view of an isometric depiction of an airfilter according to an exemplary embodiment of the invention.

FIG. 20 shows a sectional view of an air filter according to anexemplary embodiment of the invention.

FIG. 21 shows a sectional view of an air filter according to anexemplary embodiment of the invention.

FIG. 22 shows a side view of an air filter according to an exemplaryembodiment of the invention.

FIG. 23 is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 24 is an isometric depiction of an air filter according to anexemplary embodiment of the invention.

FIG. 25 shows a sectional view of an isometric depiction of an airfilter according to an exemplary embodiment of the invention.

FIG. 26 is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 27 shows a front view of an air filter according to an exemplaryembodiment of the invention.

FIG. 28 shows a sectional view of an air filter according to anexemplary embodiment of the invention.

FIG. 29 shows a sectional view of an isometric depiction of an airfilter according to an exemplary embodiment of the invention.

FIG. 30 is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 31 shows a sectional view of an air filter according to anexemplary embodiment of the invention.

FIG. 32 shows a sectional view of an isometric depiction of an airfilter according to an exemplary embodiment of the invention.

FIG. 33 shows a sectional view of an isometric depiction of an airfilter element according to an exemplary embodiment of the invention.

FIG. 34 shows a side view of an air filter according to an exemplaryembodiment of the invention.

FIG. 35 shows a sectional view of an isometric depiction of an airfilter according to an exemplary embodiment of the invention.

FIG. 36 shows a side view of an air filter according to an exemplaryembodiment of the invention.

FIG. 37 shows a sectional view of an isometric depiction of an airfilter according to an exemplary embodiment of the invention.

FIG. 38 is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 39 shows a side view of an air filter according to an exemplaryembodiment of the invention.

FIG. 40 shows a sectional view of an isometric depiction of an airfilter according to an exemplary embodiment of the invention.

FIG. 41 is an isometric depiction of an air filter element according toan exemplary embodiment of the invention.

FIG. 42 is an isometric depiction of an air filter with a housing cover,an air filter element, and a housing body according to an exemplaryembodiment of the invention.

FIG. 43 shows an isometric depiction of an additional filter element foran air filter according to an exemplary embodiment of the invention.

FIG. 44 shows a central sectional depiction of an air filter with ahousing body, a housing cover, and an inserted filter element accordingto an exemplary embodiment of the invention.

FIG. 45 shows an exploded view of the components of the air filter shownin FIG. 44 according to an exemplary embodiment of the invention.

The depictions in the figures are schematic and not true to scale.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Wherever the same reference numerals are used below, these refer toelements that are the same or similar.

FIG. 1 shows an air filter element 200 or main element 200 of an airfilter. The air filter element 200 has a plurality of filter folds 220;each filter fold 220 is composed of a first fold leaf 230 and a secondfold leaf 240. The filter folds 220 or the first fold leaves 230 andsecond fold leaves 240 here extend in a direction from the inflowdirection 270 to the outflow direction 280 or vice versa. The fold edge225 of each filter fold 220 extends perpendicular to the inflowdirection 270 and outflow direction 280. The fold edge 225 hereconstitutes the transition from a first fold leaf to a second fold leafand is formed at both the upstream surface 275 and the downstreamsurface 285 of the air filter element 200.

The fold edge 225 at the upstream side or upstream surface 275 is formedby an upstream fold leaf edge 231 of the first fold leaf 230 and anupstream fold leaf edge 241 of the second fold leaf 240. Analogously, afold edge 225 at the downstream surface 285 is formed by a downstreamfold leaf edge 232 of the first fold leaf 230 and a downstream fold leafedge 242 of the second fold leaf 240.

A fold leaf edge 260, i.e. the upstream fold leaf edge 231 or downstreamfold leaf edge 232 of the first fold leaf 230 or the upstream fold leafedge 241 or downstream fold leaf edge 242 of the second fold leaf 240,is formed by the fact that a fold leaf meets up with the filter fold bymeans of the fold edge of the fold leaf, i.e. the fold edges of two foldleaves form the filter fold 220.

A lateral fold leaf edge 233 of the first fold leaf 230 and a lateralfold leaf edge 243 of the second fold leaf 240 extend from the upstreamsurface 275 to the downstream surface 285.

The filtering action of the air filter element 220 is achieved by thefact that a filter medium is used to form the filter folds 220 andunpurified air—so-called dirty air—flows in the inflow direction 270against the upstream surface 275 and passes through the filter medium inthe direction toward the downstream surface 285 in the outflow direction280 and in so doing, is cleaned so that clean air is present at thedownstream surface 285.

The fold edges 225 of all of the filter folds 220 at the upstreamsurface 275 and downstream surface 285, respectively, form a so-calledenvelope 265; the one envelope 265 can in particular be an envelopingsurface of the fold edges at the upstream surface or downstream surface.

The fold edges 225 span the upstream surface and downstream surfacealike; the envelope corresponds to the one of these two surfaces thatspatially encloses or surrounds a functional component.

In this case, this is a connecting line of the fold edges 225 at thedownstream surface 285 or at the upstream surface 275; the connectingline extends perpendicular to the fold edges and in particular, theconnecting line, together with the downstream surface or upstreamsurface, forms a one-dimensional concave surface or form.

In this case, a one-dimensional concave surface has only one curvaturein one direction. For example, this curvature of the one-dimensionalconcave surface in one direction is produced by the fact that the folddepths of adjacent filter folds steadily decrease or steadily increaseso that the fold edges 225 have a variable distance from the respectiveopposite surface, i.e. the upstream surface 275 or downstream surface285. The envelope 265 and the fold edges 225 thus form aone-dimensionally curved concave surface since the one-dimensionalconcave surface is curved in the direction of the envelope 265, but hasno curvature in the direction of the shape of the fold edges 225.

Glue lines 235 extend in the folds in a direction from the upstreamsurface to the downstream surface and provide for an increased stabilityof the filter medium.

FIG. 2 shows a side view of an air filter element 200 with a pluralityof filter folds 220. The envelope 265 at the downstream surface 285 isembodied by the fact that the fold edge 225 of each filter fold 220 isspaced a different distance apart from the upstream surface 275. Theso-called fold depth 250 here extends in the direction of the envelope265, steadily decreasing or increasing, depending on the direction fromwhich it is viewed. Adjacent filter folds can, however, naturally havethe same fold depth 250.

In other exemplary embodiments, however, the envelope 265 can also beembodied so that the fold depth of adjacent filter folds first decreasesand then increases again. Generally, the envelope 265 can assume anyshape and in so doing, can be embodied so that an upstream surface 275or downstream surface 285 of the air filter element 200 corresponds toor is adapted to the external circumstances dictated by the design of anair filter or air filter housing.

As shown in FIG. 2, the dirty air flows in the inflow direction 270against the upstream surface 275, then penetrates into the filter folds220, is distributed along the air flow direction 610 so that the air onthe inflow side passes through the first fold leaf 230 and the secondfold leaf 240 of each filter fold 220 and is thus filtered so that thefiltered air exits the air filter element 200 at the downstream surface285 in the outflow direction 280; the air on the downstream side of theair filter element 200 is referred to as clean air.

FIG. 3 shows a sectional view of an air filter 100; the air filter 100has a housing body 110 and a housing cover 120, which togetherconstitute the housing of the air filter.

Inside the housing, there are an air filter element 200 and a functionalcomponent 300, both arranged for filtering the air flowing through. Theair filter element 200 is situated in the housing body 110, is retainedby two retaining surface recesses 190, and fixes the position of the airfilter element 200 inside the housing body 110. The air filter element200 also has a seal 205, which at least provides a sealed closure of thehousing body 110 with the air filter element. In addition, the seal 205can provide a seal between the housing body 110 and the housing cover120 and/or between the air filter element 200 and the housing cover 120.The seal 205 can be positioned or fastened to both the air filterelement 200 and the housing body 110 or housing cover 120.

It is essential to the function of the seal 205 that unfiltered air bepermitted to travel through the air filter element 200 and arrive at theclean air connection 140. The seal should also seal the housing of theair filter 100, at least to a large extent. This means that air passesthrough the dirty air connection 130 or first inflow opening 130 intothe housing of the air filter 100, passes through the air filter element200 and functional component 300 contained therein, and exits thehousing of the air filter as filtered, clean air at the clean airconnection 140 or outflow opening 140 of the air filter 100.

The seal 205 in this case is situated between the housing body 110, thehousing cover 120, and the air filter element 200 to prevent unfilteredair from penetrating into the housing of the air filter, which wouldallow it to exit the housing at the clean air connection 140 withoutflowing through the filter medium of the air filter element 200 andbeing cleaned.

The housing body 110 has an air filter element receptacle 150 in which aso-called filter collar 207 can engage. The filter collar 207 isembodied so as to mechanically affix the air filter element 200 to thehousing body.

The air flow of the air, which is to be cleaned and filtered in the airfilter 100 shown in FIG. 3, travels via or through the dirty airconnection 130, the air filter element 200, the functional component300, and the clean air connection 140. In the process, the air iscleaned essentially by the air filter element 200, exits the latter atthe downstream surface 285, and then exits the housing of the air filter100 via the functional component 300.

The functional component 300 here can be an additional filter element oranother functional component that is accommodated inside the housing ofthe air filter 100.

FIG. 4 shows a sectional view of a main element 200 or air filterelement 200 and a functional component 300 in the form of an additionalfilter element 310 folded in a star shape, viewed along the section lineA-A from FIG. 3. In particular, FIG. 4 shows that the functionalcomponent 300 is adapted to fit in or against the envelope 265 of theair filter element 200.

In this case, both the main element 200 and the functional component inthe form of an additional filter element 310 have filter folds 200 withvariable fold depths; the fold depth of the respective filter folds arematched to one another so that the envelope 265 of the downstreamsurface 285 of the air filter element 200 corresponds to the envelope265 of the upstream surface 301 of the functional component 300 or theupstream surface 311 of the additional filter element 310.

The air flow through the main element 200 and the functional component300 is routed so that the air to be cleaned at the upstream surface 275of the main element 200 penetrates into this upstream surface, thenexits the main element 200 at the downstream surface 285, and then atthe upstream surface 311 of the additional filter element 310 penetratesinto the additional filter element and exits the latter at thedownstream surface 312.

FIG. 5A shows a cross-section through an air filter element 200; thedownstream surface 285 has a semicircular free volume; the semicircularfree volume excludes only a part of the downstream surface 285 and thissemicircular free volume is formed by the envelope 265.

FIG. 5B shows the cross-section of an air filter element 200; thedownstream surface 285 has a sawtooth-shaped cross-section. Thesawtooth-shaped cross-section here extends over the entire width of theair filter element 200. The envelope 265 connects the fold edges 225 ofthe filter folds of the filter medium 210.

It should in particular be noted that the number of filter folds is notpredetermined or influenced by the shape and cross-sectional dimensionsof the downstream surface 285, i.e. the shape of the envelope 265.

As shown in FIG. 5B, in all of the exemplary embodiments described aboveand below, the air filter element 200 can have a multitude of filterfolds; the filter folds and the number of filter folds are not preset ordetermined by the shape or cross-section of the envelope 265.

FIG. 5C shows an elliptical, semicircular shape of the envelope 265 ofthe downstream surface 285 of the air filter element 200. In this case,the semicircular, elliptical shape of the envelope 265 extends acrossthe entire width of the air filter element 200 and across the entirewidth of the downstream surface 285.

FIG. 5D shows an air filter element 200 whose downstream surface 285extends in such a way that a filter fold depth steadily decreases orincreases in one direction of the envelope 265. In this case, theenvelope 265 of the fold edges at the downstream surface can extend inthe form of a hyperbola, thus producing a concave form of the downstreamsurface 285. The envelope can, however, also extend in a line, i.e. theenvelope has no curvature and is therefore an envelope line.

FIG. 5E shows an air filter element 200 whose downstream surface 285 isstepped; the steps of the downstream surface 285 are connected to oneanother via a semicircular shape of the envelope 265.

FIG. 5F shows an air filter element 200 whose downstream surface 285extends trapezoidally in such a way that the filter fold depth of themiddle filter folds 220 is greater than the fold depth of the filterfolds at the edge of the cross-sectional depiction. Here, in the regionsof increasing fold depth starting from the edges toward the middle ofthe air filter element 200, the envelope 265 of the downstream surfacecan extend in a linear or curved fashion.

FIG. 5G shows an air filter element 200 whose upstream surface 275 has astepped shape and whose downstream surface 285 has a region with a folddepth that decreases in linear fashion and a region with a constant folddepth. As a result, the envelope has a trapezoidal shape; thetrapezoidal shape of the envelope can be symmetrical or asymmetrical.

As shown in FIGS. 5F and 5G, the upstream surface 275 and downstreamsurface 285 can have any shape or any envelope of the fold edges.

The shapes of the upstream surface 275 and downstream surface 285 asshown in FIGS. 5A through 5G can also be used in fluted filters.

The cross-sections of the air filter element 200 shown in FIGS. 5Athrough 5G and the shapes of the envelope 265 are exemplary,non-exhaustive enumerations of possible forms of the envelope 265.Instead, a continuously variable fold depth of the filter folds canproduce any shape of the envelope 265 of the fold edges at the upstreamsurface 275 or downstream surface 285, but it is also possible at boththe downstream surface 285 and upstream surface 275 to produce anydesired shape of the envelope 265 on the corresponding surface.

FIGS. 5A through 5G each show the free volume or free volumes 500 asshaded areas; the free volumes of each are embodied so that theydescribe the spatial difference relative to a block-shaped air filterelement, starting from one of the air filter elements as described aboveand below.

FIG. 6 shows a side view of a fluted filter element 600; the downstreamsurface 285 extends along the envelope 265 so that the filter chambers605 each have a different filter chamber depth.

The fluted filter element 600 is characterized by the fact that thefilter chambers 605 are open and closed in alternating fashion on theupstream surface 275 and downstream surface 285. As a result, the airflow direction 610 extends through the fluted filter element 600 so thatthe incoming air on the upstream surface 275 penetrates into the filterchambers 605 that are open toward the upstream surface 275, thenpenetrates through the filter medium 210 into the adjacent filterchambers 605, which are closed on the upstream surface and are open onthe downstream surface 285, where the air exits the fluted filterelement 600.

The upstream surface 275 in a fluted filter element is composed of theupstream openings of the filter chambers and analogously, the downstreamsurface 285 is composed of the downstream openings of the filterchambers.

In the depiction shown in FIG. 6, the filter chambers 605 of the flutedfilter element 600 are distinguished in particular by the fact that theyhave different filter chamber depths in a direction from the upstreamsurface 275 to the downstream surface 285.

FIG. 7 shows an air filter element 200, which is functionally related tothe functional component 300 such that the air filter element 200 on thedownstream surface 285 is shaped so that at least a part of the airfilter element 200 presses and fixes the filter collar 207 of thefunctional component 300 along a pressing direction 305.

This makes it possible, for example, to hold the functional component inits position inside the housing of the air filter or to position itthere in the first place.

The envelope of the downstream surface 285 of the air filter element 200and the envelope of the upstream surface 301 of the functional component300 are each formed so that they have a corresponding or analogousshape. In particular, this ensures that the volume or space of thehousing of the air filter is efficiently used and the main element 200,the functional component 300, and the additional filter element 310 havethe largest possible filter area, i.e. the largest possible surface areaof the filter medium.

FIG. 8 shows an isometric view of an air filter element 200, afunctional component 300, and a housing body 110 of an air filter.

The air filter element 200 has a circumferential filter collar 207,which engages in the air filter element receptacle 150 of the housingbody 110 when the air filter element is inserted into the housing body.The air filter element receptacle 150 likewise engages in theindentation 294 of the support element. At the filter collar 207 and airfilter element, a seal 205 is also mounted along the filter collar sothat the seal 205 seals the housing body 110 against the housing body110 upon insertion of the air filter element 200.

The air filter element 200 has a filter medium 210 and this filtermedium is folded so that a free volume 500 is formed at the downstreamsurface of the air filter element in the direction of the functionalcomponent 300; the envelope 265 surrounds the free volume 500.

A support element 290 or the support structure 290 with the indentation294 extends perpendicular to the fold edges 225 of the filter medium 210in order to close the filter folds in a sealed fashion at their lateralopenings so that no unfiltered air can flow past and bypass the filterfolds of the filter. Another purpose of the support element 290 orsupport structure 290 is to stabilize the air filter element 200 and thefilter medium 210. The support element 290 also makes it possible toposition and fix the air filter element 200 during its insertion intothe housing body 110 and after the insertion into the housing body 110.

The retaining surface recess 190 of the housing protrusion 194 positionsthe air filter element 200; the retaining surface recess 190 is adaptedto the shape of the envelope 265 of the air filter element 200 or of theindentation 294. Upon insertion of the air filter element 200 into thehousing body 110, the retaining surface recess 190 engages in theindentation 294 of the support element 290 and positions and fixes theair filter element in the housing body.

The retaining surface recess 190 can, for example, be situated on thehousing protrusion 194; the housing protrusion can be a recess of thehousing body wall from the outside inward so that this recess engages inthe free volume 500 or in the indentation 294.

The support element 290 also has a first retaining surface 291, a secondretaining surface 292, and a third retaining surface 296; the firstretaining surface 291 is embodied to be received by a retaining surfacerecess 191 in the housing body 110; the second retaining surface 292 isembodied to be received by a retaining surface recess 192; and the thirdretaining surface 296 is embodied to be received by a retaining surfacerecess 196 in the housing body.

As a result, when the air filter element is inserted into the housingbody, the air filter element 200 rests via the retaining surfaces 291,292 on or against the retaining surface recesses 191, 192 in the housingbody 110.

The functional component 300 is embodied in the form of a circularcylinder and protrudes from the outflow opening 140 into the interior ofthe housing body 110. In this case, an axial direction of the functionalcomponent 300 extends parallel to the outflow direction at thedownstream surface 285 of the air filter element 200 and parallel to anaxial direction of the outflow opening 140. In addition, the outflowdirection at the downstream surface 285 of the air filter element 200 isparallel—or at least at an acute angle—to an axial direction of theoutflow opening 140. That is, the axial direction of the functionalcomponent extends in the direction of the filter edges of the downstreamsurface of the main element 200. In other words, the outflow opening 140is therefore situated on the housing body 110 facing the downstreamsurface 285 of the air filter element 200. As a result, a main air flowdirection between the air filter element 200 and the outflow opening 140is not changed and remains the same when the air flows via thedownstream surface and through the outflow opening.

The air filter element has the free volume 500 in order to provide spacefor the functional component on the interior of the housing body whenthe air filter element 200 is inserted.

FIG. 8A shows an air filter element 200, a functional component 300, anda housing body 110. The functional component is a cylinder with acircular base whose axial direction extends parallel to the shape of thefilter edges of the downstream surface 285.

The outflow opening 140 in this case is situated on a wall of thehousing body 110 so that starting from the downstream surface 285, theair flow must be deflected in order to pass through the outflow opening140.

FIG. 9 shows a sectional view of a housing body 110 with an air filterelement 200 and a functional component 300 of the kind shown in FIG. 8;the functional component and the air filter element are inserted intothe housing body.

The functional component 300 is placed against the outflow opening 140in a sealed fashion. As a result, air exiting the air filter element 200at the downstream surface 285, must flow through the functionalcomponent in order to be able to exit the housing body via the outflowopening 140.

The air filter element 200 connected to the housing body 110 in a sealedfashion by means of the seal 205 and the filter folds 220 each have arespective fold depth in such a way that the filter folds enclose thefunctional component 300.

It should in particular be noted that the fold edges or each fold edgein and of itself do/does not have a curved shape, i.e. the fold edgesextend perpendicularly into or out of the plane of the drawing.

FIG. 9A shows a sectional view of a housing body 110 with an air filterelement 200 and a functional component 300 as shown in FIG. 8A; thefunctional component and air filter element are inserted into thehousing body.

In this case, the functional component extends in the free volume 500 ofthe air filter element, parallel to the filter edge shape on thedownstream surface 285, i.e. in a direction extending out from the planeof the drawing or in a direction extending into the plane of thedrawing.

FIG. 9B shows a sectional depiction along the section line A-A from FIG.9A.

As is clearly evident, the functional component extends in the freevolume 500. In this case, the functional component can have any lengthinside the free volume 500; the greatest possible use of thethree-dimensional volume of the free volume 500 by the functionalcomponent is accompanied by an increased surface area of the functionalcomponent, for example a filter area of an additional filter element,which makes it possible to improve the overall functional performance ofthe functional component or additional filter element.

FIG. 10 shows an isometric view of a housing body with an inserted airfilter element 200. The air filter element 200 has two support elements290, which are each situated laterally on the air filter element 200 andperpendicular to the fold edges 225 of the upstream surface 275.Naturally the fold edges of the downstream surface likewise extendperpendicular to the support elements 290.

Analogous to FIG. 10, FIG. 10A is an isometric view of the housing bodywith the inserted air filter element 200 from FIGS. 8A, 9A, and 9B. Itis clear that the outflow opening 140 is situated on a wall of thehousing body 110 that extends perpendicular to the shape of the filterfolds on the upstream surface 275 and extends in a corresponding fashionon the downstream surface 285. The volume that is available in thehousing body 110 due to the free volume 500 in the air filter element200 is used so that both the functional component 300 and the mainelement 200 are situated inside the housing body and in the mainelement, a maximum filter area of the filter medium is achieved.

FIG. 11A shows an isometric view of an air filter element 200; thesupport element 290 at the downstream surface 285 has a shapecorresponding to that of the envelope 265.

FIG. 11B shows a functional component 300, which corresponds to theshape of the envelope 265 of the air filter element 200 from FIG. 11A.

FIG. 11C shows a housing body 110, which is embodied to accommodate thefunctional component 300 and the air filter element 200 from FIGS. 11Band 11A.

In this case, the housing body 110 has a plurality of locking elements115 for locking a housing cover to the housing body. The housing body110 also has an outflow opening and a clean air connection 140.

The sawtooth shape of the surface of the functional component 300 fromFIG. 11D and the corresponding shape of the envelope 265 of thedownstream surface 285 of the air filter element 200 from FIG. 11A makeit possible for the functional component 300 to have an enlarged surfacearea and therefore an improved filter performance in comparison to aplanar or flat functional component and nevertheless, more efficient useis made of the available volume inside the housing body 110.

FIG. 12A shows an air filter element 200 with a support structure 290.

At the downstream surface 285, the support structure 290 has a shapeextending along the envelope 265. In addition, the support structure 290has a first retaining surface 291 and a second retaining surface 292;the indentation 294 is located or positioned between the first retainingsurface 291 and the second retaining surface 292. The indentation 294essentially corresponds to the shape of the envelope 265 a free volume500 of the air filter element. The first retaining surface and secondretaining surface are embodied to fix the air filter element 200 via thesupport structure 290 to the housing body of the air filter and/or toposition it relative to this housing body.

Because of vibrations of the filter medium of the air filter element 200during the filtering process, the filter medium should be prevented fromcoming into contact with the housing body of the air filter sinceotherwise, the filter medium could be damaged. The first retainingsurface 291 and second retaining surface 292 therefore serve to positionthe air filter element 200, without allowing the filter medium to comeinto contact with the housing body.

FIG. 12B shows a functional component 300, which corresponds to theshape of the envelope 265 of the air filter element 200 from FIG. 12A.

FIG. 13A is an isometric depiction of an air filter element 200. Thesupport element 290 in this case extends along a plane 293, which isspanned by the vectors 293 x and 293 y.

As a result, the plane 293 of a support structure 290 extends so thatthe fold edges of the upstream surface 275 and downstream surface 285are oriented perpendicular to the plane 293 of the support elements 290of an air filter element 200.

The envelope 265 of the downstream surface 285 corresponds to a shape ofthe indentations 294 in the support element 290. Like the firstretaining surface 291 and second retaining surface 292, the indentations294 serve to fix and position the air filter element inside the housingbody.

FIG. 13B shows a functional component 300, which corresponds to theshape of the envelope 265 of the downstream surface 285 of the airfilter element 200 from FIG. 13A.

FIG. 13C shows an air filter element 200 in which the downstream surface285 extends in planar fashion between the support elements 290. Thefilter edges of the air filter element extend as part of a plane on thedownstream surface 285; this means that the fold depths of all folds ofthe air filter element are the same.

The fold depths and the positions of the fold edges at the downstreamsurface 285 and the downstream surface 285 itself are, in and ofthemselves, arranged so that the downstream surface 285, together withall of the fold edges associated with it, is recessed from the firstretaining surface 291, the second retaining surface 292, and theindentations 294 in a direction toward the upstream surface 275. Thismeans that starting from the downstream surface 285, the retainingsurfaces 291, 292 and the indentations 294 extend in the flow directionthat points away from the downstream surface. As a result, the retainingsurface 291, 292 can protrude deeper into a housing body of an airfilter than the filter medium or the fold edges of the downstreamsurface 285 do.

The downstream surface 285 can be embodied so that the fold edges of thefilter medium that are situated on it are situated at exactly the sameheight as the indentations 294.

FIG. 13D shows an air filter element 200 analogous to the air filterelement 200 in FIG. 13C; in FIG. 13D, the downstream surface 285 is notsituated at the height of the indentations 294, but instead is spaced acertain distance apart from the indentation.

As a result, when inserted into a housing body, not only do theretaining surfaces 291, 292 protrude from the air filter element 200deeper into the housing body than the downstream surface 285, but someof the support elements 290 do so as well.

The FIGS. 13C and 13D also show a design of an air filter element inwhich the downstream surface 285 is closer to the upstream surface 275than the retaining surfaces 291, 292 and indentations 294 and in whichthe upstream surface 285 is situated between the upstream surface 275and the retaining surfaces 291, 292 and indentations 294 in a flowdirection of the air through the air filter element 200.

It should be noted that the distance of the downstream surface 285 fromthe retaining surfaces 291, 292 and indentations 294 of the supportelements can be variably embodied and, for example, can be adapted tothe circumstances and structural requirements inside the housing body.

FIG. 14 shows a sectional view of an air filter 100. The housing 105 iscomposed of the housing cover 120 and the housing body 110; the housingbody and the housing cover are affixed to each other and locked by meansof locking elements 115 and a seal 205 seals the housing between thehousing body and housing cover.

Inside the housing body is the main element 200 or air filter element200 whose downstream surface has the shape of the envelope 265 andcorresponds to the form of the functional component 300. The functionalcomponent 300 is connected to the housing body 110 by means of thefilter collar 207.

The air that has flowed through the air filter element 200 and thefunctional component 300 exits the air filter 100 through the outflowopening 140.

FIG. 15 is an isometric depiction of an air filter 100 in which the airfilter has a housing body 110, a housing cover 120, and locking elements115 for locking the housing body to the housing cover. The housing cover120 is provided with a first inflow opening 130 and the housing body 110is provided with an outflow opening 140. The dirty air flows through theinflow opening 130 into the air filter or housing, is filtered in theair filter, and exits the air filter through the outflow opening orclean air connection 140.

FIG. 16 shows a sectional view of an isometric depiction of the airfilter 100 from FIG. 15. The air filter element 200 is situated insidethe housing body 110; the air that is to be filtered passes through theair filter element 200 from the direction of the inflow opening 130 andexits the housing body through the outflow opening or clean airconnection 140.

In the region of the outflow opening 140, the air filter element 200 hasa free volume 500. In the region of the free volume 500, the fold edges225 on the downstream surface 285 of the air filter element 200 form anenvelope and consequently a free volume of the air filter element; theprofile of the air filter element or the shape of the envelope on thedownstream surface is adapted to the position and outflow direction ofthe clean air connection 140 so that there are no abutting edges andthere is no sharp deflection of the air flow exiting the air filterelement 200 at the downstream surface. Through reciprocal matching ofthe position of the outflow opening 140 and the geometry of the airfilter element 200, i.e. the shape and size of the free volume 500, itis possible to optimize the air flow through the air filter and insidethe housing of the air filter and to reduce a pressure loss in the airflowing through the air filter.

The free volume 500 therefore permits the air flow to first exit the airfilter element 200 at the downstream surface and then to flow in thedirection of the outflow opening 140; the free volume 500 can be adaptedto the position and size of the outflow opening 140. In this case, theair filter element 200 with folds of variable fold depths can counteracta loss of filter area since the free volume 500 is only adapted to thesize of the outflow opening 140 and a reduction of the fold depth is notpresent in all filter folds.

FIG. 17 shows a sectional view of the air filter from FIG. 16. As isclearly evident, the outflow opening 140 has a circular shape and theenvelope 265 extends so that the free volume 500 is adapted to shape andgeometry of the outflow opening 140. This ensures that the air flowingthrough the air filter element 200 has exited the filter folds on thedownstream surface before the air flow is deflected in the direction ofthe outflow opening 140. In particular, an improved deflection of theair flow occurring at the downstream surface of the air filter element200 can be achieved by the fact that the support structure also extendsalong the envelope 265. The free volume 500 thus constitutes a chamberor cavity inside the housing body 110, in which the air flow, whichtravels perpendicular to the fold edges 225 at the downstream surface285 when exiting the air filter element 200 is deflected so that the airflow travels parallel to the shape of the fold edges 225 at thedownstream surface 285 since the outflow opening 140 requires a shape ofthe air flow that is parallel to the fold edges.

FIG. 18 shows an isometric view of an air filter element 200 with asemicircular free volume 500. The air filter element 200 from FIG. 18corresponds to the embodiment of the air filter element 200 in FIGS. 15through 17.

The support structure 290 has a first retaining surface 291 and a secondretaining surface 292; an indentation 294 is situated between theretaining surfaces 291, 292 and this indentation 294 corresponds to theshape of the envelope 265 or correlates to the shape of the envelope265.

FIG. 19 shows an air filter with a housing body 110 in which a flowstraightener 510 protrudes through a wall of the housing body into theinterior of the air filter and housing body.

The flow straightener 510 can, for example, be a so-called inflow tulip,which protrudes into the housing so that the outflowing air is calmedbefore it passes a mass air flow meter 515, i.e. a uniform air flow isachieved without the mass air flow meter having to be spaced a greatdistance apart from the housing wall.

To ensure reliable measurement results of the mass air flow meter 515,it is important for the air flowing past the mass air flow meter to befree of turbulence and free of irregular air flows or air flow paths.For this reason, if a mass air flow meter is provided, the air flowingpast must be flowing in a uniform fashion. This can be achieved, forexample, by using a flow straightener in the form of a tube; the airflowing through this tube flows essentially in one flow direction sothat the flowing air flows through this tube without turbulence. Inaddition, turbulence can be reduced by a grid 511 (only indicatedschematically in FIG. 19) mounted in the tube.

If the filtered air exits the air filter element 200 at the downstreamsurface, then this air in the filter in FIG. 19 must first be deflectedsince the outflow opening 140 is oriented orthogonal to the outflowdirection of the air. This deflection of the air flow causes turbulence,which means that the mass air flow meter 515 cannot be mounted directlyat the outflow opening or in its immediate vicinity or in the clean airconnection 140 where the air flows into the outflow opening.

Because the flow straightener or inflow tulip 510 protrudes into thehousing and housing body 110, the mass air flow meter can be mounted inthe vicinity of the housing wall of the housing body 110 and it isnevertheless possible to provide a flow-free flow in the vicinity of themass air flow meter.

The free volume 500 of the air filter element 200 can be adapted inaccordance with the geometric form of the flow straightener 510. As aresult, the envelope 265 of the fold edges at the downstream surface ofthe air filter element 200 is adapted to a cross-section of the flowstraightener 510.

In other words, the inflow tulip can also be situated centrally in awall of the housing body and is surrounded by the air filter element ina ring or half-ring, which makes it possible to select a maximum sizefor the filter area of the air filter element and as a result, theinflow tulip protruding into the housing body does not cause anysignificant loss in filter area. Not all of the fold depths of thefilter folds are adapted to the installation position of the flowstraightener; the only filter folds with a lower fold depth are thosethat coincide with the cross-sectional area of the flow straightener.

For example, the mass air flow meter 515 can be a hot film mass air flowmeter. In this case, a mass air flow measurement takes place through achange in the electrical resistance in a metal film; air flows past thismetal film and causes it to cool, which changes the resistance of themetal film, thus making it possible to measure the air mass flow rate.

FIG. 20 shows a side view of a housing body 110 with a housing cover120; an air filter element 200 is situated in the housing body.

The housing body 110 has two housing ribs 520 or housing support ribs520, each with a respective retaining surface 521. The housing ribs 520extend in a longitudinal direction between the upstream surface anddownstream surface of the air filter element 200. In this case, thehousing ribs 520 protrude into the housing body 110 in the direction ofthe shape of the fold edges of the filter folds, i.e. perpendicular tothe upstream surface and downstream surface and in the direction of thesupport element 290 of the air filter element 200.

The housing support ribs 520 serve to reinforce the dimensionalstability of the housing body 110. The housing ribs 520 can penetrate avariable depth into the housing body and can even extend through thehousing body in the direction of the fold edges.

The housing ribs 520 have a retaining surface 521; this retainingsurface is embodied to accommodate an indentation 294 of the supportelement 290 of the air filter element 200 and thus to position and fixthe air filter element 200 inside the housing body 110. Placing theindentation 294 against the retaining surface 521 ensures that thefilter folds do not come into contact with the housing support ribs;instead, the housing support ribs 520 are contacted only by the supportstructure 290.

FIG. 21 shows a sectional depiction along the section line B-B from FIG.20. The housing ribs 520 each protrude laterally into the housing body110 and air filter element 200. As illustrated above, the penetrationdepths of the housing ribs 520 are of variable dimensions and can also,for example, be embodied as continuous from one housing wall to anotherhousing wall.

FIG. 22 shows a side view of a housing body 110 with a housing cover120. The housing body 110 has two the housing support ribs 520; a firsthousing support rib 520 has a first retaining surface 521 and a secondhousing support rib 520 has a second retaining surface 521.

The housing support ribs 520 can have different heights, i.e. spans inthe longitudinal direction between the upstream surface and downstreamsurface of the inserted air filter element, and entirely differentgeometric dimensions, e.g. widths.

FIG. 23 shows an isometric view of an air filter element 200 thatmatches the housing body 110 from FIG. 22.

The air filter element 200 has two free volumes 500; a first free volume500 and first indentation 294 are formed by a first retaining surface291 and second retaining surface 292, respectively, while a second freevolume 500 and second indentation 294 are formed by the second retainingsurface 292 and another retaining surface 291, respectively.

FIG. 24 is an isometric depiction of an air filter with a housing body110; the housing body 110 has a single housing support rib 520.

The explanations given for FIGS. 20 through 23 apply analogously to theembodiment of the air filter shown in FIG. 24, with the difference thatFIG. 24 shows only a single housing support rib 520.

Naturally, as described above and below, a housing body 110 can alsohave a plurality of housing support ribs 520, in particular more housingsupport ribs than are shown here in the drawings, i.e. it can, forexample, have three or more housing support ribs.

FIG. 25 shows a sectional view of an isometric depiction of the airfilter from FIG. 24.

FIG. 25 shows how the housing support ribs 520 engage in the air filterelement 200 and, via the support structure 290, fix the air filterelement 200 in the housing body 110. In this case, the housing supportribs 520 engage in the free volume 500 of the support structure 290 orair filter element 200 from two sides.

FIG. 26 is an isometric depiction of an air filter element 200 that isanalogous to the depiction in FIG. 25.

The air filter element 200 has two support elements 290, which aresituated perpendicular to a shape of the fold edges 225 on the upstreamsurface 275 and downstream surface 285.

At the support elements 290 and the air filter element 200, the envelope265 forms an indentation 294 or a correlating free volume 500 for thehousing support ribs 520; the indentation 294 is formed by the firstretaining surface 291 and second retaining surface 292.

FIG. 27 shows an air filter 100 with a housing body 110 and a housingcover 120, which are attached to each other by means of locking elements115. Inside the housing body 110, in front of the outflow opening 140, aresonator 520 or cavity resonator geometry 530 is provided, which isembodied to reduce the flow noise of the air flowing through thehousing.

FIG. 28 shows a sectional view of an air filter along the section lineA-A from FIG. 27.

The resonator 530 is situated inside the housing body 110, in the freevolume 500 extending along the envelope 265 at the downstream surface ofthe air filter element 200.

An air filter element with filter folds of variable fold depths makes itpossible to mount a resonator inside the housing body and to maximizethe filter area of the filter medium of the air filter element at thesame time. The resonator 530 is therefore situated directly at theoutflow opening 140 or directly in front of the connection to anexternal clean air line. This makes it unnecessary to subsequentlyattach the resonator to the clean air line or the dirty air line outsidethe housing and at the same time, reduces the available filter area ofthe air filter element 200 to only a minimal degree since the freevolume 500 is adapted to the dimensions of the resonator 530.

FIG. 29 shows a sectional view of an isometric depiction of an airfilter with a housing body 110 and a housing cover 120; a resonator 530and an air filter element 200 are situated inside the housing body 110.In this case, the air filter element 200 has a free volume 500; the freevolume 500 is adapted to the spatial dimensions of the resonatorgeometry 530. In addition, i.e. in a region of the housing body that isnot occupied by the resonator geometry 530, the filter folds of the airfilter element 200 have an unreduced filter fold depth, so that thefilter area of the filter medium is only minimally reduced by themounting of the resonator 530 inside the housing body 110.

FIG. 30 is an isometric depiction of an air filter element 200 fromFIGS. 27 through 29. As is clearly evident, the downstream surface 285and the support elements 290 of the air filter element have a freevolume 500 in accordance with the shape of the envelope 265; the freevolume 500 is embodied to accommodate a resonator.

In addition, the support elements 290 have a respective first retainingsurface 291 and second retaining surface 292 situated on them; anindentation of the support element 290 correlating to the free volume500 is situated or formed between the retaining surfaces 291, 292.

FIG. 31 shows an air filter 100; an air filter element 200 and a baffledevice 540 or baffle ribs 540 are situated in the housing body 110.

The baffle device 540 has a plurality of baffle ribs; each baffle ribhas a baffle surface 541 and a baffle surface edge 542.

The individual baffle ribs of the baffle device 540 are arranged so thatthey cover a projected area of the downstream surface 285 of the airfilter element in order to thus prevent or reduce turbulence orirregularities in the air flow downstream of the downstream surface. Asa result, attaching a baffle device 540 makes it possible to reduce thedistance of a mass air flow meter 515 from the housing body 110 in theoutflow opening 140.

The baffle surface edges 542 of the individual baffle ribs combined toform an envelope, which corresponds to the envelope 265 of thedownstream surface 285 of the air filter element 200. This makes itpossible for the volume inside the housing body to be optimally parceledout to the air filter element 200 and the baffle device 540 since thefold depth of the filter folds is adapted to the shape of the bafflesurface edges 542 of the individual baffle ribs of the baffle device540.

As opposed to variable filter fold depths, with an air filter elementthat has a constant filter fold depth, the depth of the filter foldswould have to be oriented on that of the filter fold with the smallestfilter fold depth. This would result in a significant loss of filterarea.

FIG. 32 shows a sectional view of an isometric depiction of an airfilter whose housing body 110 contains an air filter element 200 and abaffle device 540. The drawing clearly shows the adaptation of thedownstream surface of the air filter element 200 to the shape of thebaffle surfaces and to the shape of the baffle surface edges of theindividual baffle ribs of the baffle device.

FIG. 33 shows a sectional view of an isometric depiction of an airfilter element 200 with a baffle device 540.

In this case, the individual baffle ribs of the baffle device 540 areattached to the support element 290.

The deflecting function for the air flow of the baffle device 540 isshown with particular clarity in FIG. 33. The air flow exits thedownstream surface of the air filter element 200 essentially in thedirection of the shape of a filter fold 220 and is deflected by thebaffle ribs of the baffle device 540 in a direction orthogonal to theshape of the filter fold 220.

The deflecting direction of the air flow by the baffle ribs cannaturally be oriented at any angle and is adapted to the position of theoutflow opening 140 on the housing of the air filter.

It should be noted that the baffle ribs of the baffle device 540 can besituated on the support elements 290 of an air filter element 200; thebaffle ribs of the baffle device 540 can also be situated on the housingbody 110 of an air filter.

If the baffle device 540 is fastened to the housing body of an airfilter, then the air filter element can be replaced without having toreplace the baffle device 540 along with it. It may not be absolutelynecessary, for example, to replace the baffle device along with an airfilter element since the baffle device is not subject to the same amountof soiling as the air filter element whose primary task is to filterdirt particles out of the dirty air and is thus naturally subject to agreater level of soiling and wear.

FIG. 34 shows a side view of an air filter 100; the housing body 110contains an air filter element 200 and three adsorption filter elementsfor hydrocarbons 550—in particular for highly volatile hydrocarbons—thatcontain an activated charcoal material, for example.

The adsorption filter elements for hydrocarbons 550 can, for example, bea hydrocarbon adsorption unit. The adsorption filter elements forhydrocarbons 550 in this case are situated between the downstreamsurface of the air filter element 200 one the one hand and the clean airconnection 140 on the other. Free volumes in the air filter element makeit possible for the adsorption filter elements for hydrocarbons,together with the air filter element 200, to be situated in the housingbody 110, thus only reducing the filter area of the filter medium of theair filter element 200 to an insignificant degree.

In particular, the adsorption filter elements for hydrocarbons 550 canbe affixed to the housing body 110, i.e. in such a way that they areable to withstand mechanical stress.

FIG. 35 shows a sectional view of an isometric depiction of an airfilter; the housing body 110 has an air filter element 200 and threeadsorption filter elements for hydrocarbons 550. The adsorption filterelements for hydrocarbons 550 protrude into the downstream surface 285of the air filter element 200 and into the support element 290.

FIG. 36 shows an air filter 100 with a housing body 110 and a housingcover 120. The housing body 110 has a first inflow opening 130 and asecond inflow opening 131. The housing cover 120 has the outflow opening140. The air filter element 200 has a partitioned upstream surface 275;the upstream surface 275 is partitioned by a housing partition wall 561of the housing body and forms a first dirty air chamber 562 and seconddirty air chamber 563. The housing partition wall 561 has a sealingsurface 567 so that the first dirty air chamber 562 is sealed off fromthe second dirty air chamber 563.

The housing body 110 also has a housing air flow flap 560, which isembodied to basically close the second dirty air connection or secondinflow opening 131, i.e. in a first operating state. For example, thehousing air flow flap 560 can be kept in the closed position by means ofa tension spring. It is naturally possible to provide other closingmechanisms, which open the housing air flow flap when a given vacuum ispresent in the housing, thus permitting air to flow in.

In the first operating state of the air filter 100, air flows into theair filter via the first inflow opening 130, is filtered via the firstdirty air chamber 562, and exits the air filter via the outflow opening140. If the first dirty air chamber is seriously soiled or clogged, forexample because snow has been sucked into the first inflow opening 130,then a vacuum in the air filter housing increases because the outflowopening 140 continues to suck out air from the air filter. Consequentlya vacuum, for example, can build up inside the housing, as a result ofwhich the housing air flow flap 560 opens the second inflow opening 131so that air is sucked into the housing via the second inflow opening 131and second dirty air chamber 563, in which case the air filter isoperated in a second operating state.

FIG. 36 shows that the variable fold depth can also affect the upstreamsurface 275 of the air filter element 200. As opposed to the exemplaryembodiments shown above, in which the downstream surface 285 had arespective free volume, in FIG. 36, the upstream surface 275 has a freevolume.

In this connection, it should in particular be noted that both theupstream surface 275 and the downstream surface 285 can have any shapeof free volume 500 for elements inside the housing body 110 of the airfilter 100, as has also been shown in FIGS. 5F and 5G.

FIG. 37 shows a sectional view of an isometric depiction of an airfilter with a first dirty air chamber 562 and second dirty air chamber563, which are respectively supplied with air or dirty air via a firstinflow opening 130 and second inflow opening 131; the second inflowopening 131 has a housing air flow flap 560, which is embodied to permitair to flow in via the inflow opening 131 only if the first dirty airchamber 562 becomes clogged. The housing partition wall 561 partitionsthe first dirty air chamber 562 off from the second dirty air chamber563.

FIG. 38 is an isometric depiction of an air filter element 200 from theexemplary embodiments in FIGS. 36 and 37. The upstream surface 275 hastwo partial surfaces that are stepped relative to each other and areseparated by the free volume 500 in the air filter element 200 andsupport element 290. As a result, the air filter element 200 in FIG. 38has filter folds with three different filter fold depths: the filterfolds in the first part of the upstream surface 275, the filter folds inthe vicinity of the free volume 500, and the filter folds in the secondregion of the upstream surface 275.

Like the downstream end or edge of the support element 290, the upstreamend or edge of the support element 290 can naturally also have a firstretaining surface 291 and second retaining surface 292.

The retaining surfaces 291, 292 are respectively mounted to the upstreamside and downstream side of the air filter element, depending on theinsertion direction of the air filter element into the housing body. Ifthe air filter element is inserted into the housing body with theupstream surface in front, then in a preferred exemplary embodiment, theretaining surfaces 291, 292 are situated at the upstream edge of thesupport element. In another preferred exemplary embodiment on the otherhand, the retaining surfaces 291, 292 are situated at the downstreamedge of the support element if the air filter element is inserted intothe housing body with the downstream surface of the air filter elementin front.

FIG. 39 shows an air filter 100 analogous to the air filter 100 that wasshown in FIG. 36.

FIG. 36 shows the housing air flow flap 560 at the second inflow opening131 in the open state; FIG. 39 shows the housing air flow flap 560 ofthe second inflow opening 131 in the closed state. As a result, in thedepiction in FIG. 39, air is sucked into the housing of the air filter100 only via the first inflow opening 130. Conversely, in FIG. 36 air issucked in via both the first inflow opening 130 and the second inflowopening 131 as long as the first dirty air chamber 562 of the firstinflow opening 130 is not completely clogged. If the first dirty airchamber 562 in FIG. 36 is completely clogged, then air is sucked in onlyvia the second inflow opening 131 and the second dirty air chamber 563.

FIG. 36 therefore shows the air filter in the second operating state(i.e. air is being sucked in via the second inflow opening) and FIG. 39shows the air filter in the first operating state (i.e. air is beingsucked in via the first inflow opening).

Also by contrast with FIG. 36, the envelope 265 of the upstream surface275 of the air filter element does not have a stepped transition toadjacent fold edges, but rather a rounded one. The rounded shape of theenvelope 265 can be adapted, for example, to the opening movement of thehousing air flow flap 560 and can thus contribute to a further increaseof the available filter area of the air filter element.

FIG. 40 shows a sectional view of an isometric depiction of the airfilter shown in FIG. 39.

The housing partition wall 561 has a retaining surface 568; thisretaining surface is embodied to accommodate, position, and fix the airfilter element 200 in the region of a first retaining surface or secondretaining surface 291, 292 of the support element 290. It is also clearfrom FIG. 40 that the free volume 500 in the region of the upstreamsurface of the air filter element 200 downstream of the second inflowopening 131 is embodied to permit an opening of the housing air flowflap 560.

FIG. 41 is an isometric depiction of an air filter element 200 for anair filter of the kind shown in FIGS. 39 and 40. It is clearly evidentthat the envelope 265 of the upstream surface 275 and of the supportelement 290 has a rounded shape in the vicinity of the second dirty airchamber 563.

An air filter element 200 with a free volume 500 for the housingpartition wall 561 makes it possible for the first dirty air chamber 562and second dirty air chamber 563 to be partitioned off from each otherby a housing partition wall 561 with a variable height (i.e. in adirection from the downstream surface to the upstream surface); thefilter fold depth can be adapted to the height of the housing partitionwall. As a result, the size of the first dirty air chamber 562 and thesize of the second dirty air chamber 563 can be adapted to each otherand the ratio of the sizes to each other can be optimized for thespecific requirements.

In the vicinity of the second dirty air chamber 563, the support element290 has a first retaining surface 291 and a second retaining surface292; the support element 290 between the first retaining surface 291 andthe second retaining surface 292 has a rounded transition or roundedshape.

In the vicinity of the first dirty air chamber 562, the support elementhas only a first retaining surface 291.

FIG. 42 is an isometric depiction of an air filter 100 with a housingcover 120, an air filter element 200, and a housing body 110. Thehousing cover 120 has an inflow opening 130; the housing cover deflectsthe air flow from the inflow opening toward the upstream surface 275.The flow direction of the air flow through the inflow opening 130 isparallel to the upstream surface 275 and must be correspondinglydeflected by the housing cover. The housing body 110 has a housing rib520 and an outflow opening 140 at an outflow fitting 141.

The housing rib 520 can provide stability to the housing body, but theprovision of the housing rib 520 can also be dictated by otherrequirements of the installation space for the air filter 100.

The air filter element 200 has a support element 290 and circumferentialseal 205. The air filter element 200 also has a flat upstream surface275 as well as a downstream surface 285; the envelope 265 of the foldedges at the downstream surface 285 forms a free volume; the free volumeis adapted to the housing ribs 520 and its shape or the envelope of thedownstream surface, for example, has a parabolic shape.

Like the housing cover, which is embodied to deflect the flow directionof the air flow on the upstream side, i.e. from the inflow opening 130to the upstream surface 275, the outflow fitting 141 is likewiseembodied to deflect the flow direction of the air flow on the downstreamside, i.e. from the downstream surface 285 to the outflow opening 140.

It should be noted that an air flow deflection of any kind can beprovided on both the downstream side and the upstream side.

FIG. 43 shows a functional component 300, which is embodied to be usedwith the air filter 100 from FIG. 42 and the corresponding main element200 from FIG. 42.

The upstream surface 311 of the functional component 300 or additionalfilter element 310 is embodied to correspond to the free volume 500 andthe envelope 265 of the air filter element 200 in FIG. 43. Embodying thefunctional component in this way enlarges the upstream surface 311 anddownstream surface 312 of the additional filter element 310, making itpossible to increase the filter performance.

FIG. 44 shows a central sectional depiction of an air filter 100 with ahousing body 110, a housing cover 120, and an inserted filter element200. A resonator 520, e.g. a broadband resonator or cavity resonatorgeometry 530, which is embodied to reduce flow noise of the air flowingthrough, is accommodated in a space-saving way. The flow passes throughthe resonator 530 perpendicular to the plane of the drawing in FIG. 44.The resonator is situated in the free volume 500 extending along theenvelope 265 at the downstream surface of the air filter element 200.The resonator 530 is enclosed by an outer casing 600 or resonatorhousing. A part 601 of the outer casing 600 oriented toward the filterelement 200 is formed by a part of the housing wall. A part 602 of theouter casing 600 is connected to the housing wall, e.g. by means ofwelding. A resonator insert piece 603 is contained in the outer casing600.

An air filter element 200 with filter folds of variable fold depthsmakes it possible to accommodate a resonator 520 in the housing body 110and to simultaneously maximize the filter area of the filter medium ofthe air filter element 200. In FIG. 44 a few filter folds areschematically depicted with dashed lines. The fold edges 225, not shown,therefore extend perpendicular to the plane of the drawing in FIG. 44and thus parallel to the direction of the flow through the resonator530.

The free volume 500 is adapted to the spatial dimensions of theresonator 520. In addition, i.e. in a region of the housing body 110that is not occupied by the resonator 520, the filter folds of the airfilter element 200 have an unreduced filter fold depth, so that themounting of the resonator 520 on the housing body 110 reduces the filterarea of the filter medium by only a minimal amount.

FIG. 45 shows an exploded view of the components of the air filter 100shown in FIG. 44. The part 602 of the outer casing 600 or housing of theresonator 520 has a respective resonator connection 605 at each of itsopposite ends. The air flows into the resonator 520 at one connectionand flows back out again at the other connection 520. The air flowthrough the resonator 520 is separate from the air flow through thefilter element 200. In addition to the resonator 520, the housing body110 is provided with an outflow opening 140. At the opposite end, aninflow opening 130 is provided on the housing cover 120 (FIG. 44).

Preferably, the filter element 200 has a respective support structure290, which is equipped with an indentation 294, at each of the oppositeends in the flow direction of the resonator 520.

1. An air filter element having an upstream surface (275), a downstreamsurface (285), and a filter medium (210); the filter medium extendsbetween the upstream surface and the downstream surface; at least one orboth of the upstream surface and downstream surface has a recessedoffset (500) in at least some sections; a functional component, which isto be brought into a functional relationship with the air filterelement, can protrude at least partially into a free space produced bythe recessed offset (500); the functional component, which is to bebrought into a functional relationship with the air filter element, canhave a functional relationship with the recessed offset of the upstreamsurface or downstream surface.
 2. The air filter element according toclaim 1, wherein the recessed offset (500) has a one-dimensional concaveor convex form.
 3. The air filter element according to claim 1, whereinthe filter medium (210) is a folded filter medium composed of folds(220); the folds each have a respective first fold leaf (230) and secondfold leaf (240), which respectively adjoin each other at a fold edge(225) by means of a fold leaf edge (231, 241; 232, 242); the first foldleaves (230) of adjacent folds are oriented essentially parallel to eachother; the first and second fold leaves (230, 240) extend between theupstream surface (275) and downstream surface (285); and the recessedoffset (500) extends along a direction in which the fold edges (225)extend.
 4. The air filter element according to claim 3, wherein the folddepth (250) varies in a direction transverse to the direction in whichthe fold edges (225) extend.
 5. The air filter element according toclaim 4, wherein a plurality of folds (220) with variable fold depths(250) is produced from a continuous medium web.
 6. The air filterelement according to claim 1, wherein the filter element (200) has asupport structure (290) and preferably, the support structure (290) hasa recessed offset in the form of an indentation (294), which at leastpartially corresponds to a shape of the recessed offset (500) of theupstream surface or downstream surface.
 7. The air filter elementaccording to claim 6, wherein the fold leaves (230, 240) are laterallyembedded in the support structure (290) at the fold leaf edges (233,243) that do not adjoin fold leaf edges of respectively adjacent filterleaves.
 8. The air filter element according to claim 3, wherein thefolds (220) extending across the recessed offset (500) are produced froma continuous medium web.
 9. The air filter element according to claim 3,wherein adjacent fold leaves (230, 240) are reciprocally stabilized bymeans of at least one spacer device, which extends parallel to the foldleaf edges (233, 243) that do not adjoin fold leaf edges of respectivelyadjacent filter leaves.
 10. An air filter element device with an airfilter element (200) according to claim 1 and a functional component(300), wherein the functional component protrudes at least partiallyinto the free space produced by the recessed offset and there is afunctional relationship between the functional component and therecessed offset (500) of the upstream surface or downstream surface. 11.The air filter according to claim 10, wherein the functional component(300) has an interface surface (301, 302) and in at least some sections,the interface surface has a shape that corresponds to that of therecessed offset (500) of the upstream surface (275) or downstreamsurface (285).
 12. An air filter comprising an air filter housing (110),an air filter element (200), and a functional component (300), whereinthe air filter element has an upstream surface (275), a downstreamsurface (285), and a filter medium (210); the filter medium extendsbetween the upstream surface and the downstream surface; at least one orboth of the upstream surface and downstream surface has a recessedoffset (500); the functional component protrudes at least partially intothe recessed offset produced by the free space; and the functionalcomponent has a functional relationship with the upstream surface ordownstream surface of the air filter element.
 13. The air filteraccording to claim 12, wherein the air filter element is embodied as anair filter element according to one of claims 2 through
 9. 14. The airfilter according to claim 12, wherein the functional component (300) hasan interface surface (301, 302); in at least some sections, theinterface surface has a shape that corresponds to that of the recessedoffset (500) of the upstream surface (275) or downstream surface (285).15. The air filter according to claim 12, wherein the functionalcomponent (300) is embodied as an additional filter element (310) thatprotrudes at least partially into the free volume produced by therecessed offset (500); the additional filter element has an upstreamsurface (311) and a downstream surface (312); one or both of theupstream surface and downstream surface of the additional filter elementcorresponds to one or both of the upstream surface (275) and downstreamsurface (285) of the air filter element (200).
 16. The air filteraccording to claim 12, wherein the functional component (300) isembodied as a baffle device (540) that protrudes at least partially intothe free volume produced by the recessed offset (500) and the baffledevice has at least one baffle surface (541) whose baffle surface edge(542) is oriented toward the respective upstream surface (275) ordownstream surface (285) of the air filter element (200).
 17. The airfilter according to claim 12, wherein functional component (300) isembodied as a flow straightener (510); the flow straightener (510) isassociated with an air mass sensor (516) that is to be brought into afunctional relationship with the air filter element; and the flowstraightener protrudes at least partially into the free volume producedby the recessed offset (500).
 18. The air filter according to claim 12,wherein the functional component (300) is embodied as a housing supportrib (520); the housing support rib has a retaining surface (521) forretaining the air filter element; and the housing support rib protrudesat least partially into the free space produced by the recessed offset(500).
 19. The air filter according to claim 12, wherein the functionalcomponent (300) is embodied as a partition wall (561); the partitionwall protrudes partially into the housing; the partition wall protrudesat least partially into the free space produced by the recessed offset(500) and has a sealing surface (567) that divides the filter housing(105) with the air filter element (200) into two filter chambers (562,563) on the upstream side, which each have a separate inflow opening;and in particular, at least one of the inflow openings is provided witha valve device.
 20. The air filter according to claim 12, wherein thefunctional component (300) is embodied as an adsorption filter elementfor hydrocarbons (550) that protrudes at least partially into the freevolume that is produced by the recessed offset (500).
 21. The air filteraccording to claim 12, wherein the functional component (300) isembodied as a resonator geometry (530) that protrudes at least partiallyinto the free volume that is produced by the recessed offset (500).